Hey there.
I know it's bad, coming from someone had a SAC average of maybe 55 in a Biology, but I'd say you'd be fine getting a 40, as long as you continue working hard for your next assessment and your exam. My friend had a SAC average of about the mid 80s and he got a 44 for his study score.
One bad SAC score shouldn't affect your study score too much. I'd recommend just getting around it, and focusing on how you can improve for future SACs and your exam, most importantly.
If you do exceptionally well on your exam, your score can bump up your SAC marks as well. Even if you're in Year 11, you've done incredibly well for your marks. You're at the top end of your cohort, so you shouldn't have anything to worry about as long as you continue studying well.
Again, this is coming from someone who's happy to have gotten above 25, but as long as you keep doing well, and study hard, you'll get that 40 no problem